The present invention relates to an image device that transmits and receives digital broadcasting signals, and more particularly to a digital broadcasting receiver to control the image/audio output signal with the information of the input data stream. The profile and the level of the MPEG-2, Moving Picture Experts Group 2, are stated in the specifications of ISO/IEC 13818-2. The profile of the MPEG-1 AUDIO, Moving Picture Experts Group 1 AUDIO, and MPEG-2 AAC, MPEG-2 Advanced Audio Coding, are stated in the specifications of ISO/IEC 11172-3 and ISO/IEC 13818-7.
FIG. 1 is the block diagram that shows the example of the function structure of a conventional digital broadcasting receiver.
In FIG. 1, the conventional digital broadcasting receiver 100 comprises an input terminal 101, through which a digital information signal that is modulated and multiplexed for image, audio and additional data, etc. is input. The receiver 100 also comprises receiving unit 11, demultiplex unit 12, memory unit 13, analyzing control unit 14, decoding unit 15, OSD (On Screen Display) synthesizing unit 16, and output terminal 102 which outputs an output signal from the OSD unit 16.
The analyzing control unit 14 analyzes the received information data to control each unit, and to generate OSD data. Error, which occurred at modulating or transmitting, is corrected in the receiving unit 11. The desired signal of the image, audio and additional data are extracted from the multiplexed signal in the demultiplex unit 12. A program information and other information are. stored in the memory unit 13. The demultiplexed signal is decoded in the decoding unit 15. The decoded image signal and the OSD data are synthesized in a OSD synthesizing unit 16.
The processing operation of received a digital broadcasting signal in conventional digital broadcasting receiver 100 will be described.
In conventional receiver 100, digital information multiplexed with a plurality of information is input into the input terminal 101. The input digital signal is demodulated in the receiving unit 11 and generates a demodulated bit stream. Image, audio, additional information data, and other control information are included in the digital information. The control information comprises the number of the broadcasting channel, the identification number of image/audio/additional data, information about the receiving frequency of each channel, and program information such as the program name and program contents, etc. This information is used as information for selecting the channel in digital broadcasting receiver 100.
In case the digital information of the channel selected by the viewer is received, the analyzing control unit 14 controls the demultiplex unit 12 to obtain the information about the channel selected by the input digital information. The image/audio/additional data and control information are separated from the input multiplexed digital information in the demultiplex unit 12. The separated data and the control information are stored in the memory unit 13. The separated image and audio are decoded in the decoding unit 15. The decoded image is synthesized with the OSD data in the OSD synthesizing unit 16 if necessary, and is output to an external monitor screen through the output terminal 102. The decoded audio is output to an external output device, for example, speaker, etc. through the output terminal 102.
EPG, Electronic Program Guide, is used to simplify the channel selection in the multichannel broadcasting. The EPG is displayed on the monitor screen, for example, by using the OSD signal. The EPG shows the program broadcasted at present and the program that will be broadcasted in the future. The viewer can select the desired channel by selecting the program which is displayed on the monitor without selecting a channel. In case the program that will be broadcasted in the future is selected, it is possible to reserve it to watch.
In case the EPG is displayed on the monitor screen, the analyzing control unit 14 controls the demultiplex unit 12 to acquire the program information from the input digital information. EPG data is generated based on the acquired program information, and the information readout from the memory unit 13, if necessary. The generated EPG data is output to the external output device through the output terminal 102.
In case the EPG is displayed on the monitor screen, the EPG data is converted into the OSD signal and sent to the OSD synthesizing unit 16. The OSD signal is synthesized with the decoded image and output to the external output device through the output terminal 102.
In this way, the image synthesized with the OSD signal is displayed on the monitor screen.
In case the channel is selected by using EPG, the analyzing control unit 14 acquires information about the program selected by the viewer, from the memory unit 13 or the input digital information. In addition, the analyzing control unit 14 controls the demultiplex unit 12 to separate corresponding image, audio and additional data. The separated image and the audio are decoded in the decoding unit 15 and are output to the external monitor and the external output device through the output terminal 102. As a result, the program selected by the viewer is displayed on the monitor screen.
As mentioned above, in the conventional digital broadcasting receiver 100, the desired image, audio and additional data are selected from an input data stream on the basis of the control information, and the program selected by the viewer is displayed.
Receiving the image bit stream of the same resolution is only considered in the conventional digital broadcasting receiver. For example, it is not considered that the image bit stream of MP@ML, Main Profile at Main Level that is standard resolution specified in MPEG-2, changes into the image bit stream of MP@HL, Main Profile at High Level that is high resolution specified in MPEG-2 in the same channel. It is not also considered that the image bit stream of MP@HL changes into the image bit stream of MP@ML in the same channel.
In case the changing between the image bit stream of standard resolution and of high resolution occurs every scene or program in the same channel, image signal is disordered because of a difference between the numbers of picture elements per one frame. The viewer watches the program with a feeling of displeasure.
While the above was explained about the image, it is explained about the audio as follows.
Receiving the audio bit stream of the same quality is only considered in the conventional digital broadcasting receiver likewise with the image. For example, it is not considered that the audio bit stream of MPEG-1 Audio, that is standard quality specified in MPEG1, changes into the audio bit stream of MPEG-2 AAC, that is high quality specified in MPEG-2, in the same channel. It is not also considered that the audio bit stream of MPEG-2 AAC changes into the audio bit stream of MPEG-1 Audio in the same channel.
In case the changing between the audio bit stream of standard quality and of high quality occurs every scene or program in the same channel, audio signal is also disordered because of difference of encoded rate at encoding. The viewer listens to the program with a feeling of displeasure.
It is a basic object of the present invention that the disordered image or audio signal is not displayed or output if the image or audio is disordered because of changing resolution or quality.
It is another object of the present invention that the viewer can recognize the changing of image resolution or audio quality by showing it on the monitor screen.
To achieve these objects, the digital broadcasting receiver of the present invention comprises the identification information detection means for detecting the identification information of the image or the audio from the received digital information. The identification information and an identification information already stored in the identification information memory means are compared one after another. The disordered image is not displayed on the monitor screen and the disordered audio is not output by controlling means for causing the image not to be displayed and audio mute means on the basis of the comparison result.
The disordered image is not displayed on the monitor screen and the disordered audio is not output, by controlling decoding means on the basis of the comparison result or the identification information, The viewer is informed that resolution of the received signal is changed, by controlling identification information output means on the basis of the comparison result or the identification information,.
In the digital broadcasting transmitter of the present invention, the identification information that shows the image resolution and audio quality is inserted into digital information by the identification information insertion means, and the digital information with the identification information is transmitted.